target/loongarch: Fix CSR.DMW0-3.VSEG check

The previous code checks whether the highest 16 bits of virtual address
equal to that of CSR.DMW0-3. This is incorrect according to the spec,
and is corrected to compare only the highest four bits instead.

Signed-off-by: Jiajie Chen <c@jia.je>
Reviewed-by: Song Gao <gaosong@loongson.cn>
Message-Id: <20230614065556.2397513-1-c@jia.je>
Signed-off-by: Song Gao <gaosong@loongson.cn>
1 file changed